Field of the Invention
This invention relates to a pneumatically-actuated multi-needle chisel tool for use in removing rust on a metal surface, weld splashes, foundry sand or the like, or chipping or grinding surfaces of stone material, concrete or the like by intensely reciprocating a multiplicity of needle chisels projecting from the forward end of the tool.
The chisel tool of the type described herein is known, as disclosed in Japanese Patent Application Publication No. 5867/1966 assigned to the same assignee as the present application, which comprises a cylinder for housing a main body of the tool, and a piston ram, an anvil and a needle holder carrying axially slidably multiple needle chisels, mounted for slidable reciprocating movement in the rearward, intermediate and forward sections, respectively within the cylinder. These components are moved to and fro by compressed air supplied as a motive fluid such that the piston ram is forced forward to strike the anvil which is in turn propelled forward to impact against the rear ends of the needle chisels, whereby the chisels are repeatedly reciprocated for impact against a workpiece such as metal, stone material or the like to perform the chipping or grinding operation or the workpiece.
With the prior art tool of this type, heavy impact forces are very smoothly developed to provide satisfactory chipping action by needle chisels which are intensely impacted on by the anvil which is struck by the piston ram with quick propelling power. However, if desired impact forces were not provided or smooth driving were impeded for some reason or other, it would ultimately exert adverse effects on the inner wall of the cylinder and the movable parts with the result that damages would be caused on the various parts such as the wall of the chisel bearing holes in the needle holder and the rear end heads of the needle chisels.
It has been found through research by the present inventor that the cause of such undesirable phenomenon is delicate discrepancy in the operational timing between the various components such as the piston ram, anvil, needle holder and needle chisels.
By way of example, if the anvil were not returned to the proper position for receiving maximum impact force from the piston ram at the point of time when the anvil is struck by the piston ram, desired impact force would not be transmitted to the anvil. Further, if the needle chisels were not in position ready for forward movement at the point of time when the needle chisels are struck by the anvil, the impact forces by the anvil would not effectively be transmitted to the needle chisels. Particularly, if the velocities of the needle holder during its forward and rearward movements were slower than those of the needle chisels, the needle holder would be impedimental to the advancement of the chisels during their forward movement. In that case the needle chisels may sometimes move forward in unison with the needle holder with the rear end heads of the chisels sticking to the rear end of the holder, so that the required impact forces are significantly lost. The arrangement is such that during the rearward movement of the needle holder the needle chisels are retracted together with the holder and that after the holder is stopped the needle chisels continue to further retract to a predetermined position by their inertia. However, if the repulsive force for retracting the needle holder were not sufficient, on one hand there would not be sufficient inertia developed to retract the needle chisels to the desired position away from the rear end of the holder while on the other hand it would become impossible to retract the anvil to its most effective position for impact by the piston rearwardmost position. Consequently, the desired stroke could not be imparted to the needle chisels upon being struck by the anvil, resulting in reduction of the impact forces. Furthermore, if the anvil started its forward movement before the needle chisels had completed their retraction, that is, while the chisels were still in the course of rearward movement, unnecessarily great impact forces would be generated between the anvil and the chisels, resulting in increased vibration and damages to the parts. Thus, if the parts impacted against each other while they were moving in opposed directions, extraordinarily vast impact forces would be developed.
Such discrepancy in operational timings are caused by loosening or play between the various parts of the tool due to shocks which may occur during the use as well as during the manufacture and assembly of the tool. Additional causes are increased frictional forces of the needle holder, the needle chisels and the like caused by iron debris such as rusts, stone chips or the like which are incidental to chipping and grinding operations because of the environment where the tool is employed and which will inevitably enter into the forward portion of the cylinder of the tool.
With the prior art chisel tool, no consideration has been paid to the adjustability of the operational timing despite the fact that the coordination in the operational timing is of critical importance to the chisel tool of this type, as indicated hereinabove.
With this in mind the present invention has been developed. According to the present invention, the arrangement for establishing proper operational timings between the various components in a smooth manner, particularly with respect to the coordination between the needle holder and the chisels is such that the needle holder is instantly moved forward by means of pneumatic repulsive forces upon the anvil being quickly forced forward by impact power from the piston ram. When the needle holder is to be retracted, the air behind the rear end of the holder is allowed to rapidly expand to move the holder backward in an instant. As a consequence the needle chisels are caused to retract to the desired position by their inertia while the air pressure built up between the needle holder and the anvil causes the latter to rapidly retract to the desired position, whereby the smooth forward movement and proper impact power of the needle chisels is ultimately insured. In addition, the present invention provides means for ready and easy adjustment to correct any discrepancy in the operational timing and to vary the stroke of the needle chisels.